Add HPKP support

README.md

@@ -8,6 +8,7 @@ The gem will automatically apply several headers that are related to security.
 - X-Content-Type-Options - [Prevent content type sniffing](http://msdn.microsoft.com/en-us/library/ie/gg622941\(v=vs.85\).aspx)
 - X-Download-Options - [Prevent file downloads opening](http://msdn.microsoft.com/en-us/library/ie/jj542450(v=vs.85).aspx)
 - X-Permitted-Cross-Domain-Policies - [Restrict Adobe Flash Player's access to data](https://www.adobe.com/devnet/adobe-media-server/articles/cross-domain-xml-for-streaming.html)
+- Public Key Pinning - Pin certificate fingerprints in the browser to prevent man-in-the-middle attacks due to compromised Certificate Authorites. [Public Key Pinnning  Specification](https://tools.ietf.org/html/draft-ietf-websec-key-pinning-21)
 
 ## Usage
 
@@ -21,6 +22,7 @@ The following methods are going to be called, unless they are provided in a `ski
 
 * `:set_csp_header`
 * `:set_hsts_header`
+* `:set_hpkp_header`
 * `:set_x_frame_options_header`
 * `:set_x_xss_protection_header`
 * `:set_x_content_type_options_header`
@@ -51,6 +53,12 @@ This gem makes a few assumptions about how you will use some features.  For exam
     :img_src => "https:",
     :report_uri => '//example.com/uri-directive'
   }
+  config.hpkp = {
+    :max_age => 60.days.to_i,
+    :include_subdomains => true,
+    :report_uri => '//example.com/uri-directive',
+    :pins => [{:sha256 => 'b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c'}]
+  }
 end
 
 # and then simply include this in application_controller.rb
@@ -298,6 +306,24 @@ console.log("will raise an exception if not in script_hashes.yml!")
 <% end %>
 ```
 
+### Public Key Pins
+
+```
+config.hpkp = {
+  max_age: 60.days.to_i,   # max_age is a required parameter
+  include_subdomains: true, # whether or not to apply pins to subdomains
+  # Per the spec, SHA256 hashes are the only currently supported format.
+  pins: [
+    {sha256: 'b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c'},
+    {sha256: '73a2c64f9545172c1195efb6616ca5f7afd1df6f245407cafb90de3998a1c97f'}
+  ],
+  enforce: true,            # defaults to false (report-only mode)
+  report_uri: '//example.com/uri-directive',
+  app_name: 'example',
+  tag_report_uri: true
+}
+```
+
 ### Using with Sinatra
 
 Here's an example using SecureHeaders for Sinatra applications:
@@ -321,6 +347,7 @@ require 'secure_headers'
     :img_src => "https: data:",
     :frame_src => "https: http:.twimg.com http://itunes.apple.com"
   }
+  config.hpkp = false
 end
 
 class Donkey < Sinatra::Application

lib/secure_headers.rb

@@ -6,7 +6,7 @@ module Configuration
     class << self
       attr_accessor :hsts, :x_frame_options, :x_content_type_options,
         :x_xss_protection, :csp, :x_download_options, :script_hashes,
-        :x_permitted_cross_domain_policies
+        :x_permitted_cross_domain_policies, :hpkp
 
       def configure &block
         instance_eval &block
@@ -42,6 +42,7 @@ def ensure_security_headers options = {}
       self.secure_headers_options = options
       before_filter :prep_script_hash
       before_filter :set_hsts_header
+      before_filter :set_hpkp_header
       before_filter :set_x_frame_options_header
       before_filter :set_csp_header
       before_filter :set_x_xss_protection_header
@@ -61,6 +62,7 @@ module InstanceMethods
     def set_security_headers(options = self.class.secure_headers_options)
       set_csp_header(request, options[:csp])
       set_hsts_header(options[:hsts])
+      set_hpkp_header(options[:hpkp])
       set_x_frame_options_header(options[:x_frame_options])
       set_x_xss_protection_header(options[:x_xss_protection])
       set_x_content_type_options_header(options[:x_content_type_options])
@@ -136,6 +138,16 @@ def set_hsts_header(options=self.class.secure_headers_options[:hsts])
       set_a_header(:hsts, StrictTransportSecurity, options)
     end
 
+    def set_hpkp_header(options=self.class.secure_headers_options[:hpkp])
+      return unless request.ssl?
+      config = self.class.options_for :hpkp, options
+
+      return if config == false || config.nil?
+
+      hpkp_header = PublicKeyPins.new(config)
+      set_header(hpkp_header)
+    end
+
     def set_x_download_options_header(options=self.class.secure_headers_options[:x_download_options])
       set_a_header(:x_download_options, XDownloadOptions, options)
     end
@@ -168,6 +180,7 @@ def set_header(name_or_header, value=nil)
 
 require "secure_headers/version"
 require "secure_headers/header"
+require "secure_headers/headers/public_key_pins"
 require "secure_headers/headers/content_security_policy"
 require "secure_headers/headers/x_frame_options"
 require "secure_headers/headers/strict_transport_security"

lib/secure_headers/headers/public_key_pins.rb

@@ -0,0 +1,95 @@
+module SecureHeaders
+  class PublicKeyPinsBuildError < StandardError; end
+  class PublicKeyPins < Header
+    module Constants
+      HPKP_HEADER_NAME = "Public-Key-Pins"
+      ENV_KEY = 'secure_headers.public_key_pins'
+      HASH_ALGORITHMS = [:sha256]
+      DIRECTIVES = [:max_age]
+    end
+    class << self
+      def symbol_to_hyphen_case sym
+        sym.to_s.gsub('_', '-')
+      end
+    end
+    include Constants
+
+    def initialize(config=nil)
+      @config = validate_config(config)
+
+      @pins = @config.fetch(:pins, nil)
+      @report_uri = @config.fetch(:report_uri, nil)
+      @app_name = @config.fetch(:app_name, nil)
+      @enforce = !!@config.fetch(:enforce, nil)
+      @include_subdomains = !!@config.fetch(:include_subdomains, nil)
+      @tag_report_uri = !!@config.fetch(:tag_report_uri, nil)
+    end
+
+    def name
+      base = HPKP_HEADER_NAME
+      if !@enforce
+        base += "-Report-Only"
+      end
+      base
+    end
+
+    def value
+      header_value = [
+        generic_directives,
+        pin_directives,
+        report_uri_directive,
+        subdomain_directive
+      ].compact.join('; ').strip
+    end
+
+    def validate_config(config)
+      raise PublicKeyPinsBuildError.new("config must be a hash.") unless config.is_a? Hash
+
+      if !config[:max_age]
+        raise PublicKeyPinsBuildError.new("max-age is a required directive.")
+      elsif config[:max_age].to_s !~ /\A\d+\z/
+        raise PublicKeyPinsBuildError.new("max-age must be a number.
+                                          #{config[:max_age]} was supplied.")
+      elsif config[:pins] and config[:pins].length < 2
+        raise PublicKeyPinsBuildError.new("A minimum of 2 pins are required.")
+      end
+
+      config
+    end
+
+    def pin_directives
+      return nil if @pins.nil?
+      @pins.collect do |pin|
+        pin.map do |token, hash|
+          "pin-#{token}=\"#{hash}\"" if HASH_ALGORITHMS.include?(token)
+        end
+      end.join('; ')
+    end
+
+    def generic_directives
+      DIRECTIVES.collect do |directive_name|
+        build_directive(directive_name) if @config[directive_name]
+      end.join('; ')
+    end
+
+    def build_directive(key)
+      "#{self.class.symbol_to_hyphen_case(key)}=#{@config[key]}"
+    end
+
+    def report_uri_directive
+      return nil if @report_uri.nil?
+
+      if @tag_report_uri
+        @report_uri = "#{@report_uri}?enforce=#{@enforce}"
+        @report_uri += "&app_name=#{@app_name}" if @app_name
+      end
+
+      "report-uri=\"#{@report_uri}\""
+    end
+
+
+    def subdomain_directive
+      @include_subdomains ? 'includeSubDomains' : nil
+    end
+  end
+end

spec/lib/secure_headers/headers/public_key_pins_spec.rb

@@ -0,0 +1,37 @@
+require 'spec_helper'
+
+module SecureHeaders
+  describe PublicKeyPins do
+    specify{ expect(PublicKeyPins.new(max_age: 1234).name).to eq("Public-Key-Pins-Report-Only") }
+    specify{ expect(PublicKeyPins.new(max_age: 1234, enforce: true).name).to eq("Public-Key-Pins") }
+
+    specify { expect(PublicKeyPins.new({max_age: 1234}).value).to eq("max-age=1234")}
+    specify { expect(PublicKeyPins.new(max_age: 1234).value).to eq("max-age=1234")}
+    specify {
+      config = {max_age: 1234, pins: [{sha256: 'base64encodedpin1'}, {sha256: 'base64encodedpin2'}]}
+      header_value = "max-age=1234; pin-sha256=\"base64encodedpin1\"; pin-sha256=\"base64encodedpin2\""
+      expect(PublicKeyPins.new(config).value).to eq(header_value)
+    }
+
+    context "with an invalid configuration" do
+      it "raises an exception when max-age is not provided" do
+        expect {
+          PublicKeyPins.new(foo: 'bar')
+        }.to raise_error(PublicKeyPinsBuildError)
+      end
+
+      it "raises an exception with an invalid max-age" do
+        expect {
+          PublicKeyPins.new(max_age: 'abc123')
+        }.to raise_error(PublicKeyPinsBuildError)
+      end
+
+      it 'raises an exception with less than 2 pins' do
+        expect {
+          config = {max_age: 1234, pins: [{sha256: 'base64encodedpin'}]}
+          PublicKeyPins.new(config)
+        }.to raise_error(PublicKeyPinsBuildError)
+      end
+    end
+  end
+end

spec/lib/secure_headers_spec.rb

@@ -18,7 +18,7 @@ class DummyClass
     allow(subject).to receive(:request).and_return(request)
   end
 
-  ALL_HEADERS = Hash[[:hsts, :csp, :x_frame_options, :x_content_type_options, :x_xss_protection, :x_permitted_cross_domain_policies].map{|header| [header, false]}]
+  ALL_HEADERS = Hash[[:hpkp, :hsts, :csp, :x_frame_options, :x_content_type_options, :x_xss_protection, :x_permitted_cross_domain_policies].map{|header| [header, false]}]
 
   def stub_user_agent val
     allow(request).to receive_message_chain(:env, :[]).and_return(val)
@@ -30,6 +30,7 @@ def options_for header
 
   def reset_config
     ::SecureHeaders::Configuration.configure do |config|
+      config.hpkp = nil
       config.hsts = nil
       config.x_frame_options = nil
       config.x_content_type_options = nil
@@ -42,6 +43,7 @@ def reset_config
 
   def set_security_headers(subject)
     subject.set_csp_header
+    subject.set_hpkp_header
     subject.set_hsts_header
     subject.set_x_frame_options_header
     subject.set_x_content_type_options_header
@@ -71,6 +73,7 @@ def set_security_headers(subject)
         subject.set_csp_header
         subject.set_x_frame_options_header
         subject.set_hsts_header
+        subject.set_hpkp_header
         subject.set_x_xss_protection_header
         subject.set_x_content_type_options_header
         subject.set_x_download_options_header
@@ -115,6 +118,17 @@ def set_security_headers(subject)
       subject.set_hsts_header({:include_subdomains => true})
     end
 
+    it "does not set the HPKP header if disabled" do
+      should_not_assign_header(HPKP_HEADER_NAME)
+      subject.set_hpkp_header
+    end
+
+    it "does not set the HPKP header if request is over HTTP" do
+      allow(subject).to receive_message_chain(:request, :ssl?).and_return(false)
+      should_not_assign_header(HPKP_HEADER_NAME)
+      subject.set_hpkp_header(max_age: 1234)
+    end
+
     it "does not set the CSP header if disabled" do
       stub_user_agent(USER_AGENTS[:chrome])
       should_not_assign_header(HEADER_NAME)
@@ -136,6 +150,7 @@ def set_security_headers(subject)
       it "does not set any headers when disabled" do
         ::SecureHeaders::Configuration.configure do |config|
           config.hsts = false
+          config.hpkp = false
           config.x_frame_options = false
           config.x_content_type_options = false
           config.x_xss_protection = false
@@ -196,6 +211,38 @@ def set_security_headers(subject)
     end
   end
 
+  describe "#set_public_key_pins" do
+    it "sets the Public-Key-Pins header" do
+      should_assign_header(HPKP_HEADER_NAME + "-Report-Only", "max-age=1234")
+      subject.set_hpkp_header(max_age: 1234)
+    end
+
+    it "allows you to enforce public key pinning" do
+      should_assign_header(HPKP_HEADER_NAME, "max-age=1234")
+      subject.set_hpkp_header(max_age: 1234, enforce: true)
+    end
+
+    it "allows you to specific a custom max-age value" do
+      should_assign_header(HPKP_HEADER_NAME + "-Report-Only", 'max-age=1234')
+      subject.set_hpkp_header(max_age: 1234)
+    end
+
+    it "allows you to specify includeSubdomains" do
+      should_assign_header(HPKP_HEADER_NAME, "max-age=1234; includeSubDomains")
+      subject.set_hpkp_header(max_age: 1234, include_subdomains: true, enforce: true)
+    end
+
+    it "allows you to specify a report-uri" do
+      should_assign_header(HPKP_HEADER_NAME, "max-age=1234; report-uri=\"https://foobar.com\"")
+      subject.set_hpkp_header(max_age: 1234, report_uri: "https://foobar.com", enforce: true)
+    end
+
+    it "allows you to specify a report-uri with app_name" do
+      should_assign_header(HPKP_HEADER_NAME, "max-age=1234; report-uri=\"https://foobar.com?enforce=true&app_name=my_app\"")
+      subject.set_hpkp_header(max_age: 1234, report_uri: "https://foobar.com", app_name: "my_app", tag_report_uri: true, enforce: true)
+    end
+  end
+
   describe "#set_x_xss_protection" do
     it "sets the X-XSS-Protection header" do
       should_assign_header(X_XSS_PROTECTION_HEADER_NAME, SecureHeaders::XXssProtection::Constants::DEFAULT_VALUE)

spec/spec_helper.rb

@@ -7,6 +7,7 @@
   Coveralls.wear!
 end
 
+include ::SecureHeaders::PublicKeyPins::Constants
 include ::SecureHeaders::StrictTransportSecurity::Constants
 include ::SecureHeaders::ContentSecurityPolicy::Constants
 include ::SecureHeaders::XFrameOptions::Constants